Energy storage devices typically comprise a plurality of electrodes. One type of energy storage device is a battery, another is a double-layer capacitor. Double-layer capacitors, also referred to as ultracapacitors and super-capacitors, are energy storage devices that are able to store much more energy per unit weight and unit volume than traditional capacitors such as electrolytic capacitors. In part, the performance of double-layer capacitors is limited by its internal resistance. The chemistry and physics of known double-layer capacitor technology limits the maximum cell operating voltage of a double-layer capacitor to less than about 4 volts, above which destructive breakdown will occur. A typical nominal operating voltage is about 2.5–3.0 volts.
Known electrode designs include conductive carbon layers. The carbon layers are typically bonded to a conductive current collector by an adhesive/bonding layer or film. When current is passed through the electrode, the interfacial contact resistance between the adhesive/bonding layer, collector, and the electrode film creates a voltage drop and generation of heat, thus, wasting energy meant to be stored. Increased contact resistance also increases a capacitors RC time constant and, thus, its charge and discharge time.
In energy storage devices that employ electrodes comprised of a carbon cloth, one method used to reduce interfacial contact resistance utilizes coating of one side the carbon cloth with molten sprayed metal. The thermal spraying process acts to impregnate the carbon cloth with conductive metal. This provides conductive paths throughout the thickness of the carbon cloth and allows for a metal-to-metal contact between the impregnated carbon cloth electrode and a metal current collector.
It is desirable to minimize the internal resistance of energy storage devices, because, generally speaking, energy storage devices having a low internal resistance can be charged and can, in turn, deliver stored energy more quickly, at a higher power density, with increased voltage, and without excessive generation of heat.